Wrote this a long time ago. Too short for an article:
Perverted - Hentai in Japanese. But the word pervert means
deviation from normal or accepted. So, how can all guys be
perverts?

Did you ever notice that the sex scene in the movie is generally
at about the same realative place as the guitar solo in a song?

Waterproof Servos
SERVO WATERPROOFING

Using this method I tested a servo under 6" of water for half an hour with no
issues. I then put the same servo in a jar of water on my nightstand overnight.
In the morning it worked fine still completely submerged. I have heard of these
servos being reliable constantly functioning in ten feet of water and being
tested to thirty feet. The servo I did first servo was controlling my forward
gun for LMS. I did this process at work on breaks as it's a lot of work on it
for a few minutes and set it aside for a few hours. I did all my servos this way
in a couple work days. Nothing was really hard to do.

I can't claim to have invented this method. I will link to the guy I got it
from, but I improved on it somewhat. He is a robotics guy and his target was
waterproof servos that are meant to function underwater continuously. Previous
to my work my servos would glitch if shot by a water gun. This method works by
not only keeping water out of the servo, but also by replacing any places for
water to get into with something other than water or air that will not harm the
servo. Pressure should have little effect on this method as the servo will exist
as a sold for the lower half and as a liquid for the upper half.

I used silicone II tub and shower, I understand that all manners of silicone and
RTV will work. Also marine epoxy works and may actually be a superior solution,
but just try un-doing it if you ever want to hack the servo or somehow mess up.
I do question whether the silicone that is deepest inside ever really cures,
however I can't come up with a reason this would ever be a problem anyway.

First dissemble the servo completely. I was using Futaba S-148s. Make sure you
know how to put it back together (use a digital camera). There should be a top
case, a bottom case and possibly a bottom cover. Now you should have a small
motor, a potentiometer and a circuit board connecting them on the bottom. As
mine were old servos and I had run into problems with their short leads, I
de-soldered the old leads and soldered on fresh long ones. Be sure to test the
servos each time you do something to make sure they work fine. I had one solder
joint come undone and had to re-solder it midway through the process.

Now take your silicone product and squirt it from the inside of the servo out.
Try to get it into each and every nook and cranny and around every component.
Fill out until you have a silicone shape that looks like it will just fit back
into your case. I covered the lower half of the potentiometer and covered up a
few holes in the top of it. I also covered at least half of the motor case and
covered a non-screw hole in the top of the motor. Also be sure that you seal
where the motor meats the circuit board. I tried to force silicone in here. Now
put the whole assembly into the lower case, some silicone should squirt out
around the circuit board if you did it right.

Take an handy tool and evenly spread the silicone that squired out over the
exposed circuit board. If you need more add it as you want too much once again.
Once that's done put the bottom cover on and once again silicone should squirt
out the seams. Spread this silicone evenly about a quarter inch all the way
around the servo to further seal the seam. If your servo doesn't have a bottom
cover you'll have to figure out how best to do all this. Spread some silicone on
the wires for a good 1/4" or so to seal them better and prevent wear.

On my servos you now have to screw two little screws back into the motor from
the top. Once done I checked the servo for functionality. At this point I found
that some of my servos had two little holes that went from top to bottom and I
filled these with silicone and smoothed off the top. I then put the top on and
screwed it together to let it dry, overnight is best, but a couple hours seemed
to do.

For the top part of the servo we're going to use a liquid to keep water out as
the parts in there have to move a lot. I chose marine RC racing grease as I had
it on hand and it was about right. I tested some with a multimeter and found it
non-conductive. The original guy used mineral oil. Mineral oil is more prone to
leaking but otherwise works well. Marine grease is heavy and will considerably
slow the servo. However for our uses it really doesn't seem to be much of an
issue. I did not notice any appreciable delay in the short throws that we use.
It was most apparent on the rudder where it took a bit longer to throw it from
side to side, but I don't think this affected anything at all.

Once dry, take the screws back out and remove the top cover. You probably have
to pick some silicone out of the screws. At this point you can also create a
continuous rotation servo if you like (instructions not included here). Now put
marine grease under the gears, on top of the case and under the case cover. You
want enough grease in here that some squishes out when you put it back together.
You'll also want an O ring to fit around the exposed servo spindle. Now put it
carefully back together with all the gears and pins in the right place. The
cover should easily fit back on, don't force it or you might break something. I
made a continuous rotation servo accidentally by forcing it. Sometimes rocking
back and forth will help get things in place. If not take a break and try later,
getting frustrated is bad. Most of my servos went together easily, one took half
an hour of sweat and many tries to get it aligned.

Once screwed together test the servo and verify that it works right. Now clean
the grease that squired out with alcohol, but leave the grease that squired out
the spindle hole (if some did). Now take your handy dandy silicone and lay a
bead all around the case to seal the seam. Flatten it nicely, I liked mine about
1/4" wide. Let it dry again at least until it's hard to the touch.

Take your O ring and give it a nice coat of grease and put it onto the servo
spindle. Then shoot some grease down the hole in the servo spindle. Yes a screw
goes here, but the grease will seal the treads and on my servos that hole goes
all the way down. Now put whatever arm your using on and screw it down and test
and see how well it works. As a final touch I spread some silicone on the screw
heads holding the case together. It's probably best to let everything thoroughly
dry for a day or more before water testing (if you can wait).

USING OIL - FASTER SERVOS
Using mineral oil is more difficult, here's what I suggest (and what I actually
did for my first servo with grease). Drill a small hole in the servo top case.
Make sure to put it in a non critical location. Put all the gears in, put the
top case on and test to make sure it works, then seal the seam with silicone or
perhaps CA and then silicone. Dry completely.

Now use a syringe and put your oil into the top case, you'll probably have to
swish it around a bit to get all the oil in and the air out. Once you have it
filled to the brim, clean the top case, so its not oily. Now you want to plug
your hole. I used just silicone, but that was with grease. You may want to use
CA if you can and then silicone on top. The smaller the hole you can use to
squirt the stuff in the better. Then oil the O ring and put it together like
normal. I'd still use grease to seal the spindle threads though. This method
should not significantly slow the servo, but will be more prone to leakage.

Here is the guy I learned all this from. Note that he starts from not so good
ideas and progresses to better ideas towards the bottom of the page: